Families from Los Angeles to New York will dive for cover at 10.18am in each timezone as they rehearse what to do in the event of a major quake.

Local radio stations will simulate news announcers warning that a 7.8 magnitude earthquake is about to strike, while ominous rumblings will play in the background.

The en masse rehearsal is being coordinated by Shakeout, a Californian group set up to encourage awareness among people living on the San Andreas fault, a tectonic fault line that runs along the West Coast.

Major earthquakes are expected to strike the same area every 150 years but it has been nearly 300 years since southern California has been hit, prompting fears of a long-overdue quake.

Lance Webster, one of the drill organisers, told the Daily Telegraph: "The natural tendency of people who live in risk areas is to downplay the danger or ignore it. The goal of this is not to frighten people but to give them positive things they can do to prepare and survive."

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As well as practicing what to do during the initial tremors, Mr Webster said people should prepare emergency supplies of water in anticipation that a major earthquake would disrupt water pipes and road links.

More than half of the 9 million Californians due to take part are students, as schools and universities along the West Coast practice their safety procedures. Major corporations like Walmart, Target and Bank of America have also ordered their staff to take participate in the drill.

Around 300,000 people outside the United States have signed up, mainly in earthquake risk zones like southern Italy and Japan.

New Zealand organised a similar drill in September involving around 1.3 million people - a quarter of the country's population.